Benthic Invertebrate Assemblages Research Articles

Storm-event-transport of urban-use pesticides to streams likely impairs invertebrate assemblages.

Insecticide use in urban areas results in the detection of these compounds in streams following stormwater runoff at concentrations likely to cause toxicity for stream invertebrates. In this 2013 study, stormwater runoff and streambed sediments were analyzed for 91 pesticides dissolved in water and 118 pesticides on sediment. Detections included 33 pesticides, including insecticides, fungicides, herbicides, degradates, and a synergist. Patterns in pesticide occurrence reveal transport of dissolved and sediment-bound pesticides, including pyrethroids, from upland areas through stormwater outfalls to receiving streams. Nearly all streams contained at least one insecticide at levels exceeding an aquatic-life benchmark, most often for bifenthrin and (or) fipronil. Multiple U.S. EPA benchmark or criterion exceedances occurred in 40 % of urban streams sampled. Bed sediment concentrations of bifenthrin were highly correlated (p < 0.001) with benthic invertebrate assemblages. Non-insects and tolerant invertebrates such as amphipods, flatworms, nematodes, and oligochaetes dominated streams with relatively high concentrations of bifenthrin in bed sediments, whereas insects, sensitive invertebrates, and mayflies were much more abundant at sites with no or low bifenthrin concentrations. The abundance of sensitive invertebrates, % EPT, and select mayfly taxa were strongly negatively correlated with organic-carbon normalized bifenthrin concentrations in streambed sediments. Our findings from western Clackamas County, Oregon (USA), expand upon previous research demonstrating the transport of pesticides from urban landscapes and linking impaired benthic invertebrate assemblages in urban streams with exposure to pyrethroid insecticides.Electronic supplementary materialThe online version of this article (doi:10.1007/s10661-016-5215-5) contains supplementary material, which is available to authorized users.

Quantitative analysis of the ecological dominance of benthic disaster taxa in the aftermath of the end-Permian mass extinction

AbstractThe end-Permian mass extinction, the largest extinction of the Phanerozoic, led to a severe reduction in both taxonomic richness and ecological complexity of marine communities, eventually culminating in a dramatic ecological restructuring of communities. During the Early Triassic recovery interval, disaster taxa proliferated and numerically dominated many marine benthic invertebrate assemblages. These disaster taxa include the bivalve generaClaraia,Unionites,Eumorphotis, andPromyalina, and the inarticulate brachiopodLingularia. The exact nature and extent of their dominance remains uncertain. Here, a quantitative analysis of the dominance of these taxa within the fossil communities of Panthalassa and Tethys benthic realms is undertaken for the stages of the Early Triassic to examine temporal and regional changes in disaster-taxon dominance as recovery progresses. Community dominance and disaster-taxon abundance is markedly different between Panthalassic and Tethyan communities. In Panthalassa, community evenness is low in the Induan stage but increases significantly in the Smithian and Spathian. This is coincident with a significant decrease in the relative abundance and occurrence frequency of the disaster taxa, most notably of the low-oxygen-affinity taxaClaraiaandLingularia. While the disaster taxa are present in post-Induan assemblages, other taxa, including two articulate brachiopod genera, outrank the disaster taxa in relative abundance. In the Tethys, assemblages are generally more even than contemporaneous Panthalassic assemblages. We observe an averaged trend toward more even communities with fewer disaster taxa in both Panthalassic and Tethyan assemblages over time.

Influences of Natural and Anthropogenic Factors and Tidal Restoration on Terrestrial Arthropod Assemblages in West Coast North American Estuarine Wetlands

Compared to benthic and water-column invertebrate assemblages, considerably less is known about terrestrial arthropods inhabiting estuarine wetlands despite their importance to tidal wetland biodiversity and productivity. We also need to know more about how human modification of estuaries, including efforts to restore estuarine wetlands, affects these assemblages. To address this knowledge gap, we assembled data from multiple studies on terrestrial arthropod assemblages from 87 intertidal wetland sites in 13 estuaries along the west coast of North America. Arthropods were sampled between 1998 and 2013 with fallout traps deployed in wetlands for 1 to 3 days at a time. We describe patterns in the abundance and taxonomic composition of terrestrial arthropods and evaluate the relative ability of natural and anthropogenic factors to explain variation in abundance and composition. Arthropod abundance was highly variable. Vegetation assemblage, precipitation, and temperature best explained variation in arthropod abundance, while river discharge, latitude, and developed and agricultural land cover surrounding sampling sites were less important. Arthropod abundance rapidly achieved levels of reference wetlands after the restoration of tidal influence to leveed wetlands, regardless of surrounding land cover. However, arthropod assemblage composition was affected by the amount of developed land cover as well as restoration age. These results suggest that restoration of tidal influence to leveed wetlands can rapidly restore some components of estuarine wetland ecosystems but that recovery of other components will take longer and may depend on the extent of anthropogenic modification in the surrounding landscape.

Start at zero: succession of benthic invertebrate assemblages in restored former sewage channels

We analysed the development of benthic invertebrate assemblages in restored urban streams in Germany. Prior to restoration these streams were open sewers and not inhabited by benthic invertebrates except Oligochaeta. Therefore, almost all taxa recolonised the streams after restoration. Restoration included the improvement of the water quality and the hydro-morphology. Following stream restoration, benthic invertebrate assemblages are supposed to undergo a distinct succession, as new habitats have been generated. These processes are poorly understood in streams. Our study revealed succession patterns and processes of benthic invertebrate assemblages in restored streams formerly transporting sewage, with pioneer taxa being dominant in the first years and a gradual assemblage maturation. We sampled 13 sites in seven restored streams in the springs of 2012 and 2013. Seven of these sites are connected to near-natural sections, whereas six sites lack this connection. The 13 sites differ in time since restoration and were sampled between one and 20 years after restoration. Additionally, we sampled 21 near-natural sites within the catchment and 11 near-natural sites in neighbouring catchments as potential recolonisation sources. Within 1 year, the restored sites underwent succession, which led to a higher resemblance of their assemblages to those of source sites. Derived from change values and non-metric multidimensional scaling, assemblages of young restored sites changed more than assemblages of old ones. In the first years after restoration we found assemblages with high abundances of pioneer taxa, while 5 years after restoration assemblages were increasingly similar to those of the source sites and mature assemblages were observed a decade after restoration. The succession towards near-natural assemblages is influenced by the instream habitats, catchment conditions and the recolonisation sources in the surroundings. Our findings reveal that monitoring results obtained fewer than 10 years after restoration will still be influenced by ongoing succession.

Water‐level fluctuations regulate the structure and functioning of natural lakes

Summary Despite becoming one of the main pressures on aquatic ecosystems globally, understanding of the ecological impacts of altered water‐level regimes in lakes lags far behind that of other human disturbances (e.g. eutrophication, acidification). We employed a multifaceted approach to explore the potential importance of water‐level fluctuations (WLF) for the structure and functioning of littoral zones and multiple trait responses of primary producers and benthic consumers across a range of natural lakes. We found that lakes with high WLF had significantly more coarse littoral substrata with less coverage of macrophyte vegetation in the shallows than in lakes with low WLF. Lakes with high WLF also had greater proportions of motile diatom species and omnivorous benthic invertebrates in shallow waters, altered taxonomic and trophic structure of benthic consumers and more homogeneous algal and benthic invertebrate assemblages. Variation along the littoral depth gradient needs to be examined when assessing the impacts of hydrological pressures in lakes. We found that depth interacted with WLF in its effects on habitat structure and mediated the response of both producer and consumer benthic assemblages to WLF. Our results indicate that amplified WLF significantly affect both the structure and functioning of lake ecosystems. Given the growing importance of WLF as an increasingly pervasive pressure on lake ecosystems worldwide, our findings have important implications for the conservation and management of global aquatic biodiversity. Inclusion of both biological traits and sampling along a depth gradient in existing and in future monitoring programmes could improve significantly the ability to detect and predict effects of altered patterns of WLF on lake ecosystems.

Diversity patterns in subarctic stream benthic invertebrate assemblages from the Sahtu Settlement Area, Northwest Territories, Canada

Benthic invertebrate assemblages were studied across four streams in the Sahtu Settlement Region of the Northwest Territories between July 2010 and October 2011 to provide information on biotic composition and associations with habitat and temporal factors. Overall diversity was similar for all streams, although taxonomic composition varied among the streams. Within streams, richness was highest in riffle and snag (woody debris) habitats and lowest in pools and leafpacks. A substantial portion of taxa (∼25%) would have been missed if only riffles had been sampled. Nearly 88% of individuals belonged to eight taxa, with &gt;60% of individuals found in only two families (Chironomidae and Baetidae). While high within-family diversity was observed, samples were also characterized by large numbers of rare taxa, with large temporal differences in abundances. Future benthic assessments in northern streams would benefit from increased sampling effort to ensure representative samples for comparing streams or sites and approaches that target dominant families in the north (e.g., Chironomidae), which can provide a great deal of information on biodiversity when examined at the generic level. Likewise, further analysis of the seasonal compositional turnover for some assemblages may be necessary to distinguish anthropogenic responses from natural variability.

Environmental Controls on River Assemblages at the Regional Scale: An Application of the Elements of Metacommunity Structure Framework.

Understanding factors that structure regional biodiversity is important for linking ecological and biogeographic processes. Our objective was to explore regional patterns in riverine benthic invertebrate assemblages in relation to their broad positioning along the river network and examine differences in composition, biodiversity (alpha and beta diversity), and environmental drivers. We up-scaled methods used to examine patterns in metacommunity structure (Elements of Metacommunity Structure framework) to examine faunal distribution patterns at the regional extent for 168 low-mountain stream invertebrate assemblages in central Germany. We then identified the most influential environmental factors using boosted regression trees. Faunal composition patterns were compartmentalised (Clementsian or quasi-Clementsian), with little difference from headwaters to large rivers, potentially reflecting the regional scale of the study, by crossing major catchment boundaries and incorporating different species pools. While idealised structures did not vary, environmental drivers of composition varied considerably between river sections and with alpha diversity. Prediction was substantially weaker, and the importance of space was greater, in large rivers compared to other sections suggesting a weakening in species sorting downstream. Further, there was a stronger transition in composition than for alpha diversity downstream. The stronger links with regional faunal composition than with richness further emphasises the importance of considering the alternative ways in which anthropogenic stressors are operating to affect biodiversity patterns. Our approach allowed bridging the gap between local (or metacommunity) and regional scales, providing key insights into drivers of regional biodiversity patterns.

Disentangling environmental drivers of benthic invertebrate assemblages: The role of spatial scale and riverscape heterogeneity in a multiple stressor environment

It is broadly acknowledged that freshwater ecosystems are affected by multiple stressors, but the relative importance of individual stressors in impairing riverine communities remains unclear. We investigated the impacts of multiple stressors, incorporating in-stream water quality, riparian and catchment land use and stream morphology, on riverine benthic invertebrate communities, while considering the spatial scales of factors and the heterogeneity of riverscapes. We performed a stepwise regression procedure linking 21 abiotic and 20 community metrics using Generalized Linear Models on data from 1018 river sites spread across Germany. High impact stressors (e.g., nutrients and water temperature) were identified for various community metrics. Both the combination of relevant stressors and their explanatory value differed significantly across streams of different sizes and ecoregions. In large rivers, the riparian land use was less important in determining community structure compared to lower order streams. Thus, possible mitigating effects of revegetated riparian buffer strips are likely to be overwhelmed by the influence of catchment-wide land use. Our results indicated substantial variability in stressors for the range of metrics studied, providing insight into potential target parameters for effective ecosystem management. To achieve long lasting successes in managing, protecting and restoring running waters, it is of vital importance to recognize the heterogeneity of riverscapes and to consider large-scale influences.

Compositional patterns of benthic assemblages on the northwestern Ross Sea shelf, Antarctica: interacting environmental drivers operating at multiple spatial scales

A comprehensive study of mega- and macro-invertebrate benthic assemblages was conduct- ed on the northwestern Ross Sea shelf in 2004 in order to examine concurrently the energy-, disturbance-, and habitat heterogeneity-diversity hypotheses, and their relevance for identifying the environmental drivers that structure benthic assemblages in Antarctica. Five transects were sampled, each of which was divided into 3 depth strata (50-250, 250-500, 500-750 m), running perpendicular to the Victoria Land coast between Cape Adare in the north and Cape Hallett in the south. The influence of environmental variables acting on different spatial scales on benthic assem- blages was assessed, including primary productivity (large-scale), iceberg scouring (quantified on different spatial scales), and habitat heterogeneity (small- scale). Clear geographic gradients could not be established for the environmental variables or for the invertebrate assemblages, but there were strong depth- related differences in the composition of assemblages. Overall, the results suggest that a combination, and interaction, of large-scale oceanographic (i.e. surface chlorophyll a, seasonal ice cover) and local habitat (e.g. sediment sponge spicule content) variables are responsible for the patterns of benthic invertebrate assemblage composition observed in the northwestern

The links between river morphological variables and benthic invertebrate assemblages: comparison among three European ecoregions

Understanding the relationship between river natural and degraded habitats and river assemblages is crucial but yet insufficient for the desired sustainable river management. Our paper therefore compares the relation of river natural morphological features and their modification to benthic invertebrate assemblages among European ecoregions Alps, Pannonian lowland, and Dinaric western Balkan with varied natural characteristics. Morphological conditions were assessed using the habitat quality (RHQ) and modification (RHM) variables, according to Slovenian hydromorphological assessment method, and linked to benthic invertebrate assemblages using multivariate analyses. The overall results indicate markedly higher importance of RHQ variables in comparison with RHM variables for structuring benthic invertebrate assemblages, but reveal important differences among ecoregions. Predominant flow and predominant channel substrate were found among the most important RHQ variables across all ecoregions. Beside these, benthic invertebrate assemblages of the Alps were influenced most by bank variables, whereas of the Pannonian lowland by features linked directly to channel conditions. In Dinaric western Balkan a combination of bank and channel variables influenced the assemblages. Among habitat modification features artificial bank profiles appeared important across all ecoregions. However, in the Alps equal explanatory power was observed for variables water impoundment by weir/dam and bank modifications, whereas in the Pannonian lowland only for variable artificial bank material and even for none in Dinaric western Balkan. According to our findings it is important to consider habitat modification in river management, but more weight should be given to habitat quality features. Moreover, the differences among ecoregions emphasize the need for ecoregion-specific approach.

Patterns of benthic mega-invertebrate habitat associations in the Pacific Northwest continental shelf waters

As human impacts and demands for ocean space increase (fisheries, aquaculture, marine reserves, renewable energy), identification of marine habitats hosting sensitive biological assemblages has become a priority. Epifaunal invertebrates, especially the structure-forming species, are an increasing conservation concern as many traditional (bottom-contact fishing) and novel (marine renewable energy) ocean uses have the potential to displace or otherwise impact these slow-growing organisms. The differences in mega-invertebrate species assemblages between high-relief rocks and low-relief sediments are well documented and likely hold for most marine environments. In anticipation of potential development of marine renewable energy faculties off Oregon and Washington (USA), a survey of the benthic invertebrate assemblages and habitats was conducted on the continental shelf of the Pacific Northwest, using video footage collected by ROV, to more finely characterize these assemblage–habitat associations. Four main associations were found: pure mud/sand dominated by sea whips and burrowing brittle stars; mixed mud–rock (which may be further divided based on size of mixed-in rocks) characterized by various taxa at small densities; consolidated rocks characterized by high diversity and density of sessile or motile mega-invertebrates; and rubble rocks showing less diversity and density than the consolidated rocks, possibly due to the disturbance generated by movement of the unconsolidated rocks. The results of this study will help classify and map the seafloor in a way that represents benthic habitats reflective of biological species assemblage distributions, rather than solely geological features, and support conservation and management planning.

Tributaries as richness source for Oligochaeta assemblage (Annelida) of Neotropical dammed river.

Tributaries may serve as richness source for the river main channel and the zoobenthos community is a good tool to verify this kind of pattern. In this study, we aimed to characterize the benthic invertebrate assemblage in three tributaries associated to the Paraná River main channel, focusing in Oligochaeta community. We hypothesized that (i) in tributaries, Oligochaeta are richer than the main river (Paraná River) and (ii) dammed tributary (Paranapanema River) is poorly diverse than the others. Samples were conducted in Paranapanema, Baía and Ivinhema tributaries using a modified Petersen grab along three transects (samples conducted inside the tributary, in the mouth of each tributary and inside Paraná River). To analyze (i) the difference between the richness and density among the tributaries and the Paraná River and (ii) effect of each tributary transect on the Oligochaeta richness we used a nonparametric Kruskal-Wallis test. Changes in environmental variables and in richness and composition of Oligochaeta were summarized by Canonic Correspondence Analysis. It was registered 21 different benthic invertebrates taxa, being Oligochaeta assemblage with the highest density. Within Oligochaeta, Narapa bonettoi was the most abundant species, followed by Haplotaxis aedochaeta and Paranadrilus descolei. In our results we refused both hypotheses, because we did not found significant differences for richness and density between the tributaries and the main river, and also no difference between the three transects of each tributary were found. However, the tributaries less influenced by damming, especially the Baía recorded high richness. This corroborates their importance to diversity in the floodplain and the species of Oligochaeta reflect the peculiar characteristics of habitats within each tributaries.

Using modelled stream temperatures to predict macro‐spatial patterns of stream invertebrate biodiversity

Summary Stream temperature is thought to be a primary determinant of the macro‐spatial distribution of stream biota, but we lack temperature data for most streams. Past research often relied on surrogates, such as altitude, latitude, catchment area (ALCA) and air temperature to study biota–temperature relationships. However, temperature surrogates may not accurately represent the thermal environments experienced by the biota and could thus produce misleading inferences regarding such relationships. In the absence of observations, modelled stream temperature could improve both predictions and interpretations of stream biodiversity patterns. We tested this hypothesis by relating stream benthic invertebrate assemblage structure and composition at 92 reference‐quality streams to ALCA, air temperature, modelled stream temperature and measured stream temperature, that is a progression from a coarse surrogate to directly measured water temperature. Modelled stream temperatures were obtained from a U.S.A.‐wide model developed previously with data from 569 reference‐quality sites. Variation in taxonomic composition, measured with an ordination, was strongly and almost identically associated with both modelled and measured stream temperature, but was less strongly associated with ALCA and air temperature. We also built predictive niche models to assess how choice of thermal metrics affected model performance. Model performance was measured as the precision with which each model predicted the number of taxa at a site (i.e. observed‐to‐expected taxon ratios). Niche models that contained modelled or measured stream temperature were more precise than those based on air temperature and ALCA. In addition, we compared the predicted probabilities of occurrence using niche models based on both modelled and measured stream temperatures. The two produced predicted probabilities of occurrence that were statistically indistinguishable for most (79%) taxa. Finally, we calculated thermal optima for each taxon as the abundance‐weighted average of stream temperature at sites where each taxon occurred. Thermal optima produced with modelled and measured stream temperatures were almost identical. Large‐scale models of stream temperature can be sufficiently accurate and precise to detect temperature‐driven patterns in stream biodiversity and should be useful in predicting the effects of climate change and other human‐caused thermal alterations on stream biodiversity.

Lionfish alter benthic invertebrate assemblages in patch habitats of a subtropical estuary

Invasive lionfish (primarily Pterois volitans) have spread throughout the Caribbean region, Gulf of Mexico, and the Southeast US coast, and resulting impacts on reef fish populations have been well documented. We examined whether lionfish can likewise affect benthic invertebrate communities, using an in situ caging experiment, in the Loxahatchee Estuary, Florida, USA. We found that lionfish caused significant declines in the three most abundant benthic invertebrate species, driving an overall shift in assemblage composition. For example, grass shrimp (Palaemonidae) abundance was reduced by nearly 90 % in the presence of lionfish. Species richness of benthic organisms was significantly higher when lionfish were present, suggesting potentially complex emergent effects of lionfish predation on benthic assemblages. Despite the fact that this experiment was conducted in just a single location using relatively small experimental units, we show altered benthic invertebrate communities could well be an additional outcome of the lionfish invasion.

Recolonisation patterns of benthic invertebrates: a field investigation of restored former sewage channels

Summary The response of benthic invertebrate assemblages to stream restoration is the subject of numerous recent studies, but the process of recolonisation of restored river sections is still poorly understood. Field studies are often flawed by uncertainties about whether the observed species colonised the restored sections after restoration or whether they were present before restoration. We investigated restored streams in the Boye catchment in an urbanised area in Germany. The streams were formerly open sewers and thus were not inhabitable by benthic invertebrates, except for Oligochaeta. Restoration included the construction of underground sewers for wastewater and morphological remodelling of the stream bed. In the spring of 2012, we sampled seven restored former channels connected with near‐natural upstream sections, which were never used as sewage channels and are in good status morphologically, and six unconnected restored former channels. Restoration measures had been conducted between one and 19 years before sampling. Additionally, we sampled 21 near‐natural sites within the catchment and eleven near‐natural sites in neighbouring catchments. Near‐natural sites were considered to be potential source sites from which benthic invertebrates might colonise the restored sites. We recorded 128 taxa and categorised them into five dispersal classes that reflect dispersal capabilities and degree of ecological specialisation. Assemblages at restored sites were characterised by lower numbers of taxa and/or high abundance of hololimnic taxa and poorly dispersing winged species and by higher species numbers and abundance of strongly dispersing generalists. A distinct recolonisation sequence was derived from the observed patterns, in which winged, strongly dispersing generalists colonised most rapidly and were followed by hololimnic species, weakly dispersing generalists and habitat specialists. Restored sites connected with near‐natural upstream sections were colonised more rapidly than unconnected restored sites, particularly by habitat specialists. Almost 90% of the recolonisation events originated from sources within a distance of 5 km. We observed a succession from pioneer assemblages to more mature communities, which resembles that of the surrounding near‐natural sites. In conclusion, assemblages in connected, restored sites needed nine to 19 years to reach maturation, while the settlement of assemblages in unconnected sites is expected to require more time.

Quantifying ecological responses to amplified water level fluctuations in standing waters: an experimental approach

Summary Global freshwater demand is increasing dramatically, with water withdrawal rates more than tripling in the last five decades. Consequently, alteration of water level regimes, particularly in the form of amplified water level fluctuations (WLF), is rapidly becoming one of the major disturbances of aquatic ecosystems globally. However, even though the impacts of WLF are likely to be strongest in littoral zones, little is known about their effects on the structure and functioning of littoral assemblages in standing water systems. We established an experiment in large outdoor pond mesocosms to examine the effects of WLF on littoral assemblages and explore the potential for development of ecological indicators of WLF. Water level fluctuations reduced benthic algal biomass and the density and taxonomic distinctness of benthic invertebrate assemblages. Both the taxonomic and trophic structure of benthic assemblages were altered significantly in ponds with WLF and homogenized along the depth gradient. Synthesis and applications. Our results indicate that water level fluctuations (WLF) can reduce considerably the productivity and biological diversity of lake littoral zones. Given that the problem is likely to be exacerbated by predicted increases in climatic variability and enhanced demand for water and hydropower, our findings have important implications for the conservation and management of global aquatic biodiversity. We identified several specific ways that WLF modify littoral assemblages along the depth gradient. This ability to identify separate pressures is an important requirement of robust ecological assessment tools. This study confers potential for development of ecological indicators of WLF in standing waters, provides indication of sampling strategies to be employed and demonstrates the need to mitigate the most extreme water withdrawals.

The links between morphological parameters and benthic invertebrate assemblages, and general implications for hydromorphological river management

AbstractIn the last decades, hydromorphological degradation of rivers has gained more attention in river management, stressing the importance of understanding the links between hydromorphology and aquatic assemblages. The present study investigated general patterns in the response of benthic invertebrate assemblages to single morphological features along naturally diversified Slovenian rivers. The whole gradient of local habitat quality (river habitat quality, RHQ) and habitat modification (river habitat modification, RHM) features, according to the Slovenian hydromorphological assessment method, was covered. Regional natural characteristics explained the low share of RHQ and RHM variability, indicating nonregional presence of morphological features. The analysis identified predominant flow and predominant channel substrate as the most important RHQ features. We found that in contrast to RHQ features, RHM features had low explanatory power. These results suggest a weaker response of benthic invertebrate assemblages to the physical alteration itself than to the effect that the alteration exerts on habitat quality features. Variance partitioning among three environmental variable groups revealed predominantly independent effects (69%) on benthic assemblages, mostly on account of regional natural characteristics (30%) and RHQ features (31%). As benthic invertebrate assemblages are adapted to the former natural conditions, a similar modification may result in different effects with regard to regional natural differences. Therefore, the low proportion of variability, explained by RHM features, might be the consequence of joint dataset from different regions. Our study gives general implications for river management, but in order to more clearly define the significance of particular modification features, we suggest further analysis within more homogeneously defined habitats that encompass regional natural characteristics. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Spatio-temporal changes in trophic categories of infaunal polychaetes near the four wastewater ocean outfalls on Oahu, Hawaii

This study examines the effect of sewage discharge on benthic polychaete assemblages in the context of their functional trophic categories. We present data spanning 20 years of monitoring benthic invertebrate assemblages and sediment properties at all 4 primary- and secondary-treatment wastewater outfalls servicing Honolulu and the island of Oahu, Hawaii, USA. Samples collected within mandated zones of initial dilution (ZIDs) near outfall discharge sites were compared to samples collected at reference stations at varying distances away. Our findings indicate that sediment properties were not affected by the outfall discharge rate or distance from each ZID. The number of polychaete species in 4 functional trophic categories (carnivore, detritivore, omnivore, and suspension feeder) did not change with the outfall solid loading rate or with distance from each ZID, thus suggesting relatively little organic enrichment. We find no evidence of heavy organic enrichment beyond the designated ZIDs at these 4 wastewater outfalls.

Sandy rivers: a review on general ecohydrological patterns of benthic invertebrate assemblages across continents

ABSTRACTThe middle and lower sections of most large rivers have fine-grained bed sediments, which may have a strong influence on the functional and taxonomical structure of benthic invertebrates. Based on results from several studies by the authors on the faunal assemblages and habitat structures of the Paraguay–Paraná River system (Brazil, Paraguay, Argentina), from European (Rhine, Loire) River systems, and data from the literature, this review identifies general patterns which appear to have a global character. On one hand, the invertebrate assemblages largely differed between the main channel (MC) and the corresponding floodplain habitats in different sections, and also the floodplain habitats along the river channel revealed great differences in their biodiversity. On the other hand, there was a remarkable homogeneity among the main-channel sections within and even between river systems. We consider physical habitat features as the crucial variables responsible for these patterns. In cross-sections from the MC towards the floodplain habitats, grain size, organic matter content and oxygen supply change dramatically, and different floodplain habitats along the same river system may have different successional stages even at small geographical distances. The sandy structure of potamal habitats (including underwater dunes), however, provides a set of habitat features characterized by continuously changing sediment structures with well-defined grain sizes, low organic matter contents and good oxygenation, which force a set of adaptations by the invertebrates that limits but stabilizes the diversity of invertebrates in these large river sections. A better understanding of the ecohydrological interactions between habitat dynamics and benthic invertebrates is needed to improve sustainable river ecosystem management. We discuss the non-recovery of large benthic invertebrate species in the lower section of large rivers after improvement of the water quality in the context of these ecohydrological features. Conclusions are drawn for river restoration.

Anadromous sea lampreys (Petromyzon marinus) are ecosystem engineers in a spawning tributary

Summary Sea lampreys (Petromyzon marinus) disturb the substratum during nest construction and alter the physical habitat, potentially affecting other stream organisms. We quantified differences in depth, velocity, fine‐sediment coverage, embeddedness, intragravel permeability and benthic invertebrate assemblages (density and diversity) among nest mounds, nest pits and undisturbed reference locations over a 4‐month period after June spawning. In 2010 and 2011, immediate and persistent effects of nest construction were assessed in summer (July) and in autumn (late September to early October), respectively. Randomly selected nests were sampled annually (25 each in summer and autumn). Nest construction increased stream‐bed complexity by creating and juxtaposing shallow, swift, rocky habitat patches with deep, slow, sandy habitat patches. Mounds had a 50–143% less cover of fine sediment, and a 30–62% reduction in embeddedness, compared to pits and reference locations. These physical changes persisted into the autumn (almost 4 months). Five insect families contributed 74% of the benthic invertebrate abundance: Chironomidae (27%), Hydropsychidae (26%), Heptageniidae (8%), Philopotamidae (7%) and Ephemerellidae (6%). Densities of Hydropsychidae, Philopotamidae and Heptageniidae were up to 10 times greater in mounds than in pits and adjacent reference habitat. In summer, mounds had twice the density of Chironomidae than did pits, and 1.5 times more than reference habitats, but densities were similar among the habitats in autumn. These results suggest that spawning sea lampreys are ecosystem engineers. The physical disturbance caused by nest‐building activity was significant and persistent, increasing habitat heterogeneity and favouring pollution‐sensitive benthic invertebrates and, possibly, drift‐feeding fish.